Functional liver parenchyma can be damaged from treatment of liver malignancies with ⁹⁰Y selective internal radiation therapy (SIRT). Evaluating functional parenchymal changes and developing an absorbed dose (AD)–toxicity model can assist the clinical management of patients receiving SIRT. We aimed to determine whether there is a correlation between ⁹⁰Y PET AD voxel maps and spatial changes in the nontumoral liver (NTL) function derived from dynamic gadoxetic acid–enhanced MRI before and after SIRT. 

Methods: Dynamic gadoxetic acid–enhanced MRI scans were acquired before and after treatment for 11 patients undergoing ⁹⁰Y SIRT. Gadoxetic acid uptake rate (k₁) maps that directly quantify spatial liver parenchymal function were generated from MRI data. Voxel-based AD maps, derived from the ⁹⁰Y PET/CT scans, were binned according to AD. Pre- and post-SIRT k₁ maps were coregistered to the AD map. Absolute and percentage k₁ loss in each bin was calculated as a measure of loss of liver function, and Spearman correlation coefficients between k₁ loss and AD were evaluated for each patient. Average k₁ loss over the patients was fit to a 3-parameter logistic function based on AD. Patients were further stratified into subgroups based on lesion type, baseline albumin–bilirubin scores and alanine transaminase levels, dose–volume effect, and number of SIRT treatments. 

Results: Significant positive correlations (ρ = 0.53–0.99, P < 0.001) between both absolute and percentage k₁ loss and AD were observed in most patients (8/11). The average k₁ loss over 9 patients also exhibited a significant strong correlation with AD (ρ ≥ 0.92, P < 0.001). The average percentage k₁ loss of patients across AD bins was 28%, with a logistic function model demonstrating about a 25% k₁ loss at about 100 Gy. Analysis between patient subgroups demonstrated that k₁ loss was greater among patients with hepatocellular carcinoma, higher alanine transaminase levels, larger fractional volumes of NTL receiving an AD of 70 Gy or more, and sequential SIRT treatments. 

Conclusion: Novel application of multimodality imaging demonstrated a correlation between ⁹⁰Y SIRT AD and spatial functional liver parenchymal degradation, indicating that a higher AD is associated with a larger loss of local hepatocyte function. With the developed response models, PET-derived AD maps can potentially be used prospectively to identify localized damage in liver and to enhance treatment strategies.